Many trucks and commercial vehicles have service brakes which are engaged by air (pneumatic) pressure. Usually, all of the wheels of the vehicle will carry a brake which responds to pressurised air delivered along a supply line controlled by a foot pedal. The harder the foot pedal is depressed the greater the quantity of pressurised air supplied and the harder the brakes are applied.
In addition, the vehicle will have a parking brake which is engaged by a mechanical spring which acts in opposition to a pneumatic cylinder. Air pressure within the pneumatic cylinder acts to hold the parking brake in its disengaged position, whilst release of the air pressure allows the mechanical spring to engage the parking brake. Typically, the parking brake will operate upon the wheels of the rear axle of a vehicle.
In certain situations it is desired to have an automatic means of engaging the brakes of the vehicle in addition to the foot pedal or parking brake lever/pedal/switch. One example of such a situation is on a lane closure vehicle.
A lane closure vehicle is a vehicle, often a truck, which is used for the temporary closure of a lane of a road. Typically, the lane closure vehicle will carry a large arrow which directs following traffic to move out of the lane occupied by the vehicle. The vehicle may be stationary, or may move slowly along the roadway, and is generally implemented to protect road workers who may be working in or adjacent to that lane of the roadway.
While lane closure vehicles have flashing lights to alert drivers of their presence, it is possible that a driver on the road may fail to notice a lane closure vehicle before is too late to brake or to take avoiding action. The relative speed between lane closure vehicles and nearby traffic is typically large, and therefore any impact between traffic and lane closure vehicles is usually very damaging to the vehicles and their occupants. As such, most lane closure vehicles include a large deformable “cushion” (i.e. impact attenuator) at their rear, which can absorb an impact in the event a vehicle does drive into them.
Lane closure vehicles may also include an automatic braking system in addition to standard brakes. The automatic braking system activates the lane closure vehicle's brakes in the event that another vehicle drives into the lane closure vehicle. Thus, if the lane closure vehicle is moving slowly along the lane at the moment of impact and the driver is unable immediately to apply the service brakes or parking brake, the automatic braking system applies the lane closure vehicle's brakes so that the lane closure vehicle is prevented from causing a secondary accident, perhaps by being pushed into a road worker or further vehicle. One example of such a system is described in UK Patent No. 2453523.
The present invention seeks to provide an improved automatic braking system.
The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.